Rubber composition containing treated silica and products with component thereof

ABSTRACT

The invention relates to rubber compositions containing a treated silica, particularly sulfur cured rubber compositions, and articles of manufacture having a component thereof such as, for example tires. The invention particularly relates to synthetic amorphous silica, particularly a precipitated silica, treated with a combination of allylsilane and dialkylsilane.

FIELD OF THE INVENTION

The invention relates to rubber compositions containing a treatedsilica, particularly sulfur cured rubber compositions, and articles ofmanufacture having a component thereof such as, for example tires. Theinvention particularly relates to synthetic amorphous silica,particularly a precipitated silica, treated with a combination ofallylsilane and dialkylsilane.

BACKGROUND OF THE INVENTION

Rubber compositions are often reinforced with reinforcing fillers suchas at least one of rubber reinforcing carbon black and syntheticamorphous silica (e.g. precipitated silica).

Various products contain at least one component comprised of such rubbercompositions such as, for example, tires.

In order to enhance rubber reinforcing effects of precipitated silica, acoupling agent is typically used in combination with the precipitatedsilica.

Such coupling agent typically contains a moiety (e.g. alkoxysilanegroup) reactive with hydroxyl groups (e.g. silanol groups) on theprecipitated silica and another different moiety (e.g. polysulfide as asulfur contributing moiety) interactive with elastomers containingcarbon-to-carbon double bonds (e.g. diene-based elastomers).

A typical disadvantage of such polysulfide moiety of the silica couplingagent is its sulfur contribution at an elevated temperature of theuncured rubber composition, such as for example during physical mixingof the uncured rubber composition, which interacts with carbon-to-carbondouble bonds of an elastomer in the rubber composition to promote asignificantly increased viscosity of the rubber composition which leadsto increased rubber processing difficulties, or challenges. Suchphenomenon is well known to those having skill in such art.

For this invention, a rubber reinforcing precipitated silica is providedas a precipitated silica treated with a combination of allylsilane anddialkylsilane. It appears that such combination can produce asynergistic effect for the treated silica insofar as a tan deltaphysical property of a rubber composition is concerned.

A dialkylsilane for such treatment may be, for example, in a form of adialkyldihalosilane such as for example a dimethyldichlorosilane or adimethyldialkoxysilane such as, for example, a dimethyldiethoxysilane.An allylsilane for such treatment may, for example, be in a form of anallyltrialkoxysilane or allylhalosilane.

For this invention, it has been discovered that a precipitated silicatreated with a combination of allylsilane and dialkylsilane may be usedas silica reinforcement for a sulfur curable rubber composition withoutuse of a sulfur-containing silica coupling agent. Such treatedprecipitated silica does not contain a polysulfidic moiety so thatsulfur is not available to prematurely interact with the elastomer(s) inthe rubber composition.

While the mechanism might not be fully understood, where precipitatedsilica is treated with an allylsilane such as for example, anallyltrialkoxysilane or allylhalosilane, together with adialkyldihalosilane such as, for example, dimethyldichlorosilane, it isenvisioned that an alkoxysilane moiety of the allylalkoxysilane orhalogen moiety of the allylhalosilane reacts, for example, with hydroxylgroups (e.g. silanol groups) and/or hydrogen groups, particularlyhydroxyl groups, on the precipitated silica and the dialkyldihalosilane(e.g. dimethyldichlorosilane) or dialkyldialkoxysilane (e.g.dimethyldiethoxysilane) reacts with, for example, hydroxyl groups (e.g.silanol groups) on the precipitated silica to enhance the hydrophobicityof the treated silica.

The use of a combined treatment of silica with the allylsilane and thedialkyldihalosilane or dialkyldialkoxysilane has been observed inenhanced hydrophobicity of the silica over the use of the allyl silanealone. For example the allyltrichlorosilane used to treat the silica hasan area of 168.18 square angstroms when measured by molecular modelingin a hydrocarbon solvent. The dimethylsilane in a form ofdimethyldichlorosilane used in the treatment has an area of 138.30square angstroms when modeled in the same hydrocarbon environment. Thesmaller molecular size of the dimethyldichlorosilane allows for deeperpenetration into the pores of the silica surface and therefore enablesreaction with more of the hydroxyl groups present on the silica surface.It is envisioned that this enhanced hydrophobicity results in enhanceddispersion in the elastomer matrix and enhanced interaction between thesilica and the elastomer.

Accordingly, a significant aspect of this invention is an interaction ofthe combined allylsilane with said dialkyldichlorosilane ordialkyldialkoxysilane treated precipitated silica to not only provide adelayed coupling of the treated precipitated silica with diene-basedelastomer in the presence of the sulfur curative during the subsequentvulcanization of the rubber composition but to also promote an enhancedhydrophobicity of the allyl hydrocarbon treated precipitated silica todesirably cause a more efficient dispersibility of the treated silicawithin the rubber composition prior to the aforesaid promoted couplingof the treated silica to the diene-based elastomer to thereby enhanceone or more physical properties for the rubber composition.

It is further envisioned that, if desired, because of an absence ofavailable sulfur atoms in the case of where a sulfur containing couplingagent is not used to couple the silica to the elastomer, a beneficiallyrelatively high temperature mixing of the combination of allyl anddialkyl hydrocarbon treated silica with the elastomer(s) can be achievedwithout an attendant sulfur-promoted viscosity increase of the rubbermixture prior to addition of the sulfur and sulfur cure accelerators tothe rubber mixture, a higher temperature mixing of the rubbercomposition provides an opportunity for more efficient mixing of therubber composition for a shorter mixing time.

Representative examples of various allylsilanes for preparation of allylfunctionalized silica are, for example, allyltriethoxysilane,allyltrimethoxysilane, allyldimethylchlorosilane, allyltrichlorosilane,allylmethyldichlorosilane, diallylchloromethylsilane,diallyldichlorosilane and triallylchlorosilane.

In the description of this invention, the term “phr” relates to parts byweight for a material or ingredient per 100 parts by weightelastomer(s)”. The terms “rubber” and “elastomer” are usedinterchangeably unless otherwise indicated. The terms “cure” and“vulcanize” are used interchangeably unless otherwise indicated.

SUMMARY AND PRACTICE OF THE INVENTION

In accordance with this invention, a sulfur curable rubber composition(e.g. conjugated diene-based elastomer-containing rubber composition) isprovided which contains a reinforcing filler comprised of a syntheticamorphous silica (precipitated silica) in a form of a precipitatedsilica treated with a combination of an allylsilane and a dialkylsilanein a form of, for example, a dialkyldihalosilane ordialkyldialkoxysilane.

In practice the treated precipitated silica is preferably a pretreatedsilica prior to its addition to the rubber composition, although,alternatively with precipitated silica may be treated in situ within therubber composition, with said combination of allylsilane anddialkylsilane.

Alternately, said precipitated silica may be:

(A) pretreated prior to its addition to said rubber composition withsaid allylsilane and the product thereof treated in situ within saidrubber composition with said dialkylsilane, or

(B) pretreated prior to its addition to said rubber composition withsaid dialkylsilane and the product thereof treated in situ within saidrubber composition with said allylsilane.

In one embodiment of the invention, invention the treated, preferablypretreated, precipitated silica is provided as a precipitated silicatreated with a combination of:

(A) an allylsilane comprised of:

-   -   (1) an allyltrialkoxysilane, or    -   (2) allylhalosilane, and

(B) a dialkylsilane comprised of;

-   -   (1) a dialkyldihalosilane, or    -   (2) dialkyldialkoxysilane.

In one embodiment of the invention the allyl containing hydrocarbonradical for said allylsilane may be comprised of at least one of:

—CH₂—CH═CH₂,(allyl hydrocarbon radical)

—CH₂—CH═CH—CH₃,(2-butene radical)

—CH₂—CH═C—(CH₃)₂ and(dimethallyl hydrocarbon radical)

—CH₂—C(CH₃)═CH—CH₃(2-methyl-2-butene radical)

For said allylsilane, said allyltrialkoxysilane may, for example, becomprised of at least one of allyltriethoxysilane, allyltrimethoxysilaneand allyldimethylchlorosilane.

For said allylsilane, said allylhalosilane may, for example, becomprised of at least one of allyltrichlorosilane,allylmethyldichlorosilane, diallylchloromethylsilane,diallyldichlorosilane and triallylchlorosilane.

Said dialklyldihalosilane may, for example, be comprised ofdimethyldichlorosilane.

Said dialkyldialkoxysilane may, for example, be comprised ofdimethyldiethoxysilane.

In one alternative embodiment, it may be desired to first treat theprecipitated silica with the allylsilane and then treat the resultingproduct thereof with the dialkyldihalosilane or dialkyldialkoxysilane,although it is currently preferred to treat the precipitated silica withthe combination of allylsilane and dialkyldihalosilane ordialkyldialkoxysilane.

It is envisioned that a general formula for precipitated silica treatedwith a combination of the allylsilane and dialkyldihalosilane may berepresented by the general formula (I):

where Z represents the precipitated silica; R¹, R², R³, R⁴, R⁵, and R⁶are the same or different radicals comprised of an alkyl groupcontaining from 1 to 4 carbon atoms, a cycloalkyl group, a phenyl group,an alkene group containing from 3 to 18 carbon atoms or cycloalkeneradical having from 5 to 8 carbon atoms;

wherein at least one of said radicals is an allyl hydrogen containinghydrocarbon radical;

wherein a is a value in a range of from 0 to 2, b is a value in a rangeof from 0 to 2, c is a value in a range of from 1 to 3, and d, e, and fare values in a range of 0 to 3.

In further accordance with this invention, a rubber composition isprovided comprised of:

(A) at least one conjugated diene-based elastomer, and

(B) reinforcing filler comprised of:

-   -   (1) said treated silica (e.g. pretreated silica) comprised of        precipitated silica treated (e.g. pretreated) with a combination        of said allylsilane and dialkylsilane, or    -   (2) a combination of:        -   (a) said treated (e.g. pretreated) silica comprised of            precipitated silica treated (e.g. pretreated) with a            combination of said allylsilane and dialkylsilane, and        -   (b) precipitated silica without said treatment (e.g.            pretreatment) with said combination of said allylsilane and            dialkylsilane, or    -   (3) a combination of rubber reinforcing carbon black and:        -   (a) said treated (e.g. pretreated) silica comprised of            precipitated silica treated (e.g. pretreated) with a            combination of said allylsilane and dialkylsilane, or        -   (b) a combination of said treated (e.g. pretreated) silica            comprised of precipitated silica treated (e.g. pretreated)            with a combination of said allylsilane and dialkylsilane and            precipitated silica without said treatment with a            combination of said allylsilane and dialkylsilane;    -   wherein said allylsilane is an allylhalosilane or        allylalkoxysilane, and    -   wherein said dialkylsilane is a dialkyldihalosilane or        dialkyldialkoxysilane.

Said rubber composition may further contain at least one silica couplingagent to aid in coupling said precipitated silica which has not beentreated (e.g. pretreatment) with a combination of said allylsilane anddiakylsilane to conjugated diene-based elastomers contained in saidrubber composition (where said allylsilane is an allylhalosilane orallylalkoxysilane, and where said dialkylsilane is a dialkyldihalosilaneor dialkyldialkoxysilane).

Alternately, said rubber composition may further contain at least onesilica coupling agent to aid in coupling said treated (e.g. pretreated)precipitated silica comprised of a precipitated silica treated (e.g.pretreated) with a combination of said allylsilane and dialkylsilane toconjugated diene-based elastomers contained in said rubber composition(where said allylsilane is an allylhalosilane or allylalkoxysilane, andwhere said dialkylsilane is a dialkyldihalosilane ordialkyldialkoxysilane).

In practice, said silica coupling agent has a moiety (e.g. alkoxy group)reactive with hydroxyl groups on said silica (e.g. hydroxyl groups suchas silanol groups) and another different, sulfur based, moietyinteractive with elastomers contained in said rubber composition.

For example, a rubber composition is provided which is comprised of,based upon parts by weight per 100 parts by weight rubber (phr):

(A) 100 phr of at least one conjugated diene based elastomer;

(B) about 10 to about 120, alternately about 40 to about 100, phr ofreinforcing filler wherein said reinforcing filler is comprised of:

-   -   (1) about 40 to about 100, alternately about 50 to about 80, phr        of said treated (e.g. pretreated) silica, namely treated silica        comprised of precipitated silica treated (e.g. pretreated) with        a combination of allylsilane or allylalkoxysilane with said        dialkyldihalosilane or dialkyldialkoxysilane;    -   (2) zero to about 60, alternately about 3 to about 30, phr of        rubber reinforcing carbon black, and    -   (3) optionally up to about 70 phr of precipitated silica without        said treatment, namely without treatment with said combination        of said allylsilane or allylalkoxysilane with said        dialkyldihalosilane or dialkyldialkoxysilane.

In further accordance with this invention, an article of manufacture,such as for example a tire, is provided having at least one componentcomprised of said rubber composition. Such tire component may be, forexample, at least one of a tire sidewall, tire sidewall insert, tiresidewall apex, ply coat, wire coat, and tread.

From a historical perspective, according to U.S. Pat. Nos. 5,708,069,7,550,610 and 5,789,514 silica gels may be derived, for example, byhydrophobtaining a silica hydrogel with, for example, anorganomercaptosilane and alkyl silane and drying the product. Theresulting hydrophobated silica gel may be blended with natural rubberand/or synthetic rubber.

A general description of silica gel and precipitated silica may befound, for example, in the Encyclopedia of Chemical Technology, FourthEdition (1997), Volume 21, Kirk-Othmer in Pages 1020 through 1023.

While silica gels are a form of precipitated silica, this invention isintended to be a significant departure therefrom in a sense of havingthe aforesaid required BET and CTAB surfaces area characterization incombination with the required narrow ratio thereof in a range of from0.8 to 1.3 instead of significantly different precipitated silicas suchas presented in patent publication EP 0643015 and mentioned in U.S.Patent Publication No. 2008/0293871 as indicated as being useful as anabrasive and/or thickening component in toothpaste (rather than forsuitable rubber reinforcement) with a BET surface area of 10 to 130 m²/gand CTAB surface area of 10 to 70 m²/g combined with a BET to CTABsurface area ratio of approximately 1 to 5.2.

Rubber compositions are often prepared by mixing a diene-based rubber,carbon blacks and other rubber compounding ingredients, exclusive ofsulfur based rubber curatives, in at least one sequential mixing stepwith at least one mechanical mixer, usually referred to as“non-productive” mix step, or stage(s), to an elevated temperature underhigh shear rubber mixing conditions followed by a final mix step, orstage, in which sulfur based curative(s), such as sulfur and sulfur cureaccelerators, are added and mixed therewith at a lower mixingtemperature to avoid unnecessarily pre-curing the rubber mixture duringthe mixing stage. The terms “non-productive” and “productive” mix stagesare well known to those having skill in the rubber mixing art.

It is to be appreciated that the rubber composition is conventionallycooled to a temperature below about 40° C. between the aforesaid mixstages.

The sulfur vulcanizable elastomers may be comprised of, for example, atleast one of polymers of at least one of isoprene and 1,3-butadiene andcopolymers of styrene with at least one of isoprene and 1,3-butadiene.

If desired, at least one of the sulfur vulcanizable elastomers may becomprised of:

(A) a coupled elastomer comprised of a polymer of at least one ofisoprene and 1,3-butadiene and copolymer of styrene with at least one ofisoprene and 1,3-butadiene,

wherein said coupled elastomer is at least one of tin and silica coupledelastomer, or

(B) functionalized elastomer of at least one of styrene/butadienecopolymer elastomer (SBR), c is 1,4-polybutadiene elastomer and cis1,4-polyisoprene elastomer;

wherein said functionalized elastomer contains functional group(s)comprised of:

-   -   (1) amine functional group reactive with said allyl        functionalized precipitated silica, or    -   (2) siloxy functional group reactive with said allyl        functionalized precipitated silica filler rubber reinforcement,        or    -   (3) combination of amine and siloxy functional groups reactive        with said allyl functionalized silica, or    -   (4) silane/thiol functional group reactive with said allyl        functionalized silica, or    -   (5) hydroxyl functional groups reactive with said allyl        functionalized precipitated silica, or    -   (6) epoxy groups reactive with said allyl functionalized        precipitated silica, or    -   (7) carboxyl groups reactive with said allyl functionalized        precipitated silica.

The following examples are provided to further illustrate the inventionin which the amounts and percentages of materials are by weight unlessotherwise indicated.

EXAMPLE I Preparation of Treated Precipitated Silica

An evaluation of precipitated silica treated by a combination of allyltrichlorosilane and dialkyldihalosilane (namely dimethyldichlorosilane)was undertaken.

For such evaluation, the precipitated silica was pre-treated before itsaddition to a rubber composition by the following procedure used toprepare samples of allyl/dimethyl treated silica, namely precipitatedsilica treated with a combination of allyl trichlorosilane anddimethyldichlorosilane, referred to herein sometimes as “allyl” and“dimethyl”.

Approximately 400 grams of precipitated silica was added to 1.5 liter ofdry toluene in a 2 liter resin kettle equipped with a Dean-Stark trapand condenser. The silica-in-toluene suspension was stirred and heatedto reflux and the water on the silica was removed via azeotrope with thetoluene. The Dean-Stark trap collected approximately 21 ml of water. Thesuspension was then cooled under nitrogen to below 70° C. andapproximately 200 ml of triethyl amine was added to act as a scavengerfor HCl formed by the silica treatment. A mixture ofallyltrichlorosilane (e.g. 47 grams) and dimethyldichlorosilane (e.g. 23grams) in 50 ml of dry toluene was then added dropwise with stirringover 30 minutes. The mixture was stirred for 15 hours and then 0.5 literof water was added. The pH of the mixture was then adjusted to between 7and 8 using sodium carbonate. The resulting suspension was filtered,washed with water, and dried at 150° C. overnight.

EXAMPLE II Evaluation of Pre-treated Precipitated Silicas

Samples of the pretreated precipitated silica of Example I wereevaluated in a rubber composition. The following Table A represents thegeneral rubber formulation. The parts and percentages are by weightunless otherwise indicated.

TABLE A Parts Non-Productive Mix Stage (NP) Cis 1,4-polybutadienerubber¹ 0 and 30 Solution polymerized styrene/butadiene rubber (S-SBR)²0 and 70 Fatty acid³ 1 Silica coupling agent⁴ 0 and 5.2 Carbon black⁵5.2 Precipitated silica⁶ 65 Productive Mix Stage (PR) Sulfur 1.2, 1.6,and 1.8 Sulfenamide sulfur cure accelerator 1.6 and 1.5 Zinc oxide 1.5Diphenylguanidine 1.5 and 1.0 Antioxidant, amine based 0.5 ¹Cis1,4-polybutadiene rubber as Budene ™ 1207from The Goodyear Tire & RubberCompany ²Organic solution polymerization prepared styrene/butadienerubber (S-SBR) as Solflex ™ from The Goodyear Tire & Rubber Company³Mixture comprised of stearic, palmitic and oleic acids ⁴Composites ofcarbon black and coupling agents in a 50-50 weight ratio were used,although reported in the Table in terms of the coupling agent itself.The coupling agents were comprised of bis(3-triethoxypropyl) polysulfidehaving an average of from about 3.6 to about 3.8 connecting sulfur atomsin its polysulfidic bridge from Evonic Degussa as Si69 ™, sometimesreferred to as a tetrasulfide, and bis(3-triethoxypropyl) polysulfidehaving an average of from about 2.1 to about 2.3 connecting sulfur atomsin its polysulfidic bridge, sometimes referred to as a disulfide, asSi266 ™ from Evonic Degussa. ⁵Rubber reinforcing HAF (high abrasionfurnace) carbon black as N330, an ASTM designation. ⁶Precipiated silicafrom Example I as Zeosil ™ 1165 from Rhodia.

Samples of the rubber compositions were prepared by blending theingredients in an internal rubber mixer using two separate, sequential,mixing stages, or steps, namely a first non-productive mixing stage (NP)to a relatively high temperature followed by a second, productive mixingstage (PR) to a significantly lower mixing temperature in which thesulfur, sulfur cure accelerator and zinc oxide were added. Such rubbermixing procedure is well known to those having skill in such art.

For the non-productive mixing stage (NP), the ingredients are mixed forabout 4 minutes to an autogeneously generated, via the high shear mixingin the internal rubber mixer, drop temperature of about 150° C. at whichtime the batch is “dropped”, or removed, from the associated internalrubber mixer. The batch is sheeted out and allowed to cool to atemperature below 40° C. The batch is then mixed in a productive mixingstage (PR) during which free sulfur, vulcanization accelerator and zincoxide are added and mixed for a period of about 2 minutes to a droptemperature of about 110° C.

The cure behavior and various cured physical properties of therespective Samples are shown in the following Table 1. For the curedrubber Samples, the Samples were individually cured for about 30 minutesat a temperature of about 150° C.

The rubber samples are identified as Control rubber Samples A and H,without the pretreated silica, with the remainder of the rubber SamplesB through G being Experimental rubber Samples which contained various ofthe pretreated precipitated silicas. The parts and percentages are byweight unless otherwise indicated.

TABLE 1 Control Control Materials (phr) A B C D E F G H Polybutadienerubber 30  30  30  30  30  30  30 30 S-SBR rubber 70  70  70  70  70  70 70 70 Coupling agent 5.2^(a)   0   0   0   0   0   0 5.2^(h) Untreatedprecipitated silica 65   0   0   0   0   0   0 65 Treated precipitatedsilica 0  65^(b)  65^(c)  65^(d)  65^(e)  65^(f)  65^(g) 0 Sulfur 1.2  1.8   1.8   1.8   1.8   1.8   1.8 1.6 Sulphenamide accelerator 1.6  1.5   1.5   1.5   1.5   1.5   1.5 1.6 Diphenylguanidine 1.5   1   1  1   1   1   1 1.5 Test Properties MDR¹, 150° C., 60 minutes Max-Mintorque (dNm) 15.6  18.1  18.1  17.2  15.3  16.3  14.5 20.2 Tensile²,stress-strain (cured 30 min. at 150° C.) 100% ring modulus (MPa) 2.1  2.3   2.4   2.3   2.1   2   1.4 1.9 300% ring modulus (MPa) 10   8.2  8   7.5   6.5   6   3.9 7.6 Tensile strength (MPa) 18.7  14.3  13.6 14  13  11.6  12.2 15.1 Elongation at break (%) 476  471  460  495  505 484  581 486 RPA³, 0.833 Hz, 100° C., 15% strain Uncured G′ (kPa) 195 168  168  161  183  190  157 263 RPA³ - 100° C. cure cycle, 11 Hz, 10%strain Storage modulus (G′), (kPa) 1594 2005 2019 1900 1653 1737 14771835 Tan delta 0.107   0.123   0.121   0.115   0.094   0.108   0.1310.134 ¹Rheometer (MDR) instrument ²Automated Testing System (ATS)instrument ³Rubber Process Analyzer (RPA) instrument

For the above treated precipitated silicas referred to in Table 1 interms of molar ratios or percent's of allyltrichlorosilane (allyl) anddimethyldichlorosilane (dimethyl):

b—treatment=100% allyl

c—treatment=80% allyl/20% dimethyl (4/1) molar ratio

d—treatment=60% allyl/40% dimethyl (1.5/1) molar ratio

e—treatment=40% allyl/60% dimethyl (0.67/1) molar ratio

f—treatment=20% allyl/80% dimethyl (0.25/1) molar ratio

g—treatment=100% dimethyl

For the coupling agents in Table 1:

a=Composite of carbon black and silica coupling agent in a 50/50 weightratio, reported in the Table in terms of the coupling agent itself. Thesilica coupling agent was comprised ofbis(3-triethoxysilylpropyl)polysulfide having an average of from about3.6 to about 3.8 connecting sulfur atoms in its polysulfidic bridge,sometimes referred to as being a tetrasulfide, as Si69™ from EvonicDegussa.

h=Composite of carbon black and silica coupling agent in a 50/50 weightratio, reported in the Table in terms of the coupling agent itself. Thesilica coupling agent was comprised ofbis(3-triethoxysilylpropyl)polysulfide having an average of from about2.1 to about 2.3 connecting sulfur atoms in its polysulfidic bridge,sometimes referred to as being a disulfide, as Si266™ from EvonicDegusssa.

It can be seen that for Experimental synthetic rubber based rubberSamples B, C, D, E, F, and G of Table 1 the blends of silica having beentreated with only allyltrichlorosilane (experimental rubber Sample B) oronly dimethyldichlorosilane (experimental rubber Sample G) as well asvarious combinations of allyltrichlorosilane and dimethyldichlorosilane(referred to herein as allyl and dimethyl, respectively), namelyexperimental rubber Samples C, D, E and F, all exhibited lower uncuredG′ values than the control rubber Samples A and H, with a minimum valueof uncured G′ being observed for the combination of theallyltrichlorosilane and dimethyldichlorosilane in a ratio of 40/60namely for rubber Sample D.

This is considered significant in a sense that uncured G′ is animportant indicator for rubber compounding processing. As the uncured G′value goes lower, rubber processing becomes easier, namely the rubbercomposition becomes easier to process in a sense that it takes lessenergy to process.

In Table 1, the tan delta values for the allyl/dimethyl treatment show aminimum value for rubber Sample E, which used a 40/60 molar ratio ofallyltrichlorosilane (allyl) and dimethyldichlorosilane (dimethyl)treatment.

BRIEF DESCRIPTION OF DRAWING

A drawing is provided as FIG. 1 (FIG. 1) to reflect an observedrelationship of tan delta values of the rubber composition withprecipitated silica pretreated with allyltrichlorosilane (allyl) ordimethyldichlorosilane (dimethyl) individually (Samples B and G) or withwhat appears to be a synergistic combination of allyltrichlorosilane anddimethyldichlorosilane.

THE DRAWING

In FIG. 1 the tan delta values are plotted for experimental rubberSamples B through G which were reported in Table 1.

The plot of FIG. 1 shows tan delta values for experimental rubberSamples B, C, D, E, F and G which contained the precipitated silicatreated individually (Samples B and G) or with a combination of (SamplesC, D, E and F) various ratios of the allyltrichlorosilane anddimethyldichlorosilane.

It is readily observed in FIG. 1, and in this Example, that a minimumtan delta value is reached for experimental rubber Sample D whichcontained the silica pretreated with an apparent synergistic combinationof the allyltrichlorosilane and dimethyldichlorosilane with a molarratio of 60/40 (1.5/1) of allyltrichlorosilane (allyl) todimethyldichlorosilane (dimethyl).

If it is desired for the tan delta value for the rubber composition tobe about 0.12 or less, for a rubber processing advantage over rubberSamples B and G, then experimental rubber samples D, E and F appear tobe appropriate which used the precipitated silica pretreated withallyltrichlorosilane and dimethyldichlorosilane in molar ratios rangingfrom about 0.55/1 to about 9/1 as illustrated in FIG. 1 by theapproximating vertical dashed lines. It appears that a molar ratio in aregion of about 1.5/1 (about 60/40) may be an optional molar ratio wherea minimum tan delta value is desired.

The reduced tan delta values for the rubber composition, as observed inthis Example, resulting from use of the precipitated silica treated witha combination of the allyltrichlorosilane and dimethyldichlorosilane,are considered significant in a sense that the lower tan delta valuesare indicative of lower hysteresis for the rubber composition. The lowerhysteresis of a rubber composition used in a tire tread is indicative ofbetter fuel economy for an associated vehicle with a tire having a treadof such rubber composition. Accordingly, a lower tan delta for therubber composition is indicative of better fuel economy for theassociated vehicle with a tire with a tread of such rubber composition.

It is also concluded, and it is an additional significant aspect of thisinvention, that it is observed that the reported data in Table 1 for theuncured G′ data indicates that the precipitated silica treated with thecombination of both allyltrichlorosilane and dimethyldichlorosilaneresulted in significantly improved (reduced) uncured G′ values for therubber composition, for which the combination of allyltrichlorosilaneand dimethyldichlorosilane treatment of the precipitated appears have asynertistic effect, as compared to use of precipitated silica treatedindividually with the allyltrichlorosilane or dimethyldichlorosilane,namely Samples B and G, or with the untreated precipitated silica usedwith traditional silica coupling agents, namely rubber compositions Aand H.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

1. (canceled)
 2. A process of preparing a rubber composition whichcomprises adding a precipitated silica to a rubber composition comprisedof at least one conjugated diene-based elastomer wherein saidprecipitated silica is pretreated prior to its addition to said rubbercomposition with a combination of an allylsilane and a dialkylsilane,exclusive of a sulfur containing silica coupling agent, where saiddialkylsilane is in a form of a dialkyldihalosilane ordialkyldialkoxysilane.
 3. (canceled)
 4. (canceled)
 5. (canceled) 6.(canceled)
 7. (canceled)
 8. (canceled)
 9. (canceled)
 10. The process ofclaim 2 wherein said precipitated silica is first treated with saidallylsilane and the resulting product thereof treated with saiddialkyldihalosilane or dialkyldialkoxysilane.
 11. (canceled) 12.(canceled)
 13. (canceled)
 14. (canceled)
 15. (canceled)
 16. (canceled)17. (canceled)
 18. (canceled)
 19. (canceled)
 20. (canceled) 21.(canceled)
 22. The process of claim 2 wherein said rubber compositioncontains a silica coupling agent to aid in coupling said treatedprecipitated silica to said conjugated diene-based elastomer(s) wheresaid coupling agent is comprised of a moiety reactive with hydroxylgroups contained on said treated precipitated silica and anotherdifferent moiety interactive with said conjugated diene-basedelastomer(s).
 23. (canceled)
 22. The process of claim 10 wherein saidrubber composition contains a silica coupling agent to aid in couplingsaid treated precipitated silica to said conjugated diene-basedelastomer(s) where said coupling agent is comprised of a moiety reactivewith hydroxyl groups contained on said treated precipitated silica andanother different moiety interactive with said conjugated diene-basedelastomer(s).